1. Field of the Invention
The present invention relates to an optical disk drive, and more specifically, to a control circuit and method for controlling an optical disk drive.
2. Description of the Prior Art
Optical disk drives such as compact disk (CD) drives and digital versatile disk (DVD) drives are widely used storage devices. Aside from audio and video information CDs and DVDs are commonly used to store computer software and other data.
Essentially, both CD and DVD disks comprise a spiral track from which data can be read by an optical pickup head of the CD or DVD drive. During a read mode, the optical pickup head is controlled to follow the spiral groove to sequentially read data from the disk. During a seek mode, when a track or frame seek function is executed, drive electronics control the optical pickup head to move to a new frame or new track of the disk.
According to the prior art, the drive electronics reference tabulated positional data and must further decode data stored in frames of the CD or DVD disk, such as subcode data, in order to adjust the position of the optical pickup head. While the optical pickup head changes tracks, a phase-locked loop monitors an eight-to-fourteen modulation (EFM) signal to control the rotational speed of the disk. In other words, during the seek function, the optical pickup head is moved across the surface of the disk to a new location and the phase-locked loop responds accordingly. Slow response of the phase-locked loop results in the time and processing overhead required for performing the seek function becoming high enough to affect overall seek time and performance of the CD or DVD drive.
In many cases, such as high-speed (32X–48X+) CD-ROM drives, a limiting factor in drive data read rate is data seek time. This is further apparent in non-sequential or random access of the frames of a CD-ROM disk. The high-speed potential of the CD-ROM drive is negated by a longer than necessary seek time, and the drive spends much of its operational time delivering data at rates more in line with low-speed drives (8X–16X). This problem also exists in other types of CD and DVD drives to varying degrees, and typically, additional time and processing overhead is required to overcome it.
Please refer to FIG. 1. FIG. 1 shows a phase-locked loop 10 for controlling a CD or DVD drive according to the prior art. A frequency detector 12 and a phase detector 14 receive an EFM signal and a data phase-locked loop (DPLL) signal. A filter 16 accepts error signals output from the frequency detector 12 and the phase detector 14. The filter 16 outputs a control signal to a voltage-controlled oscillator (VCO) 18 that produces a corresponding oscillating signal at a frequency relating to the input control signal. A frequency divider 20 divides the oscillating signal and outputs the DPLL signal to the frequency detector 12 and the phase detector 14. The phase-locked loop 10 locks onto a component frequency of the EFM signal to regenerate a clock signal to facilitate synchronized reading of data from the optical disk as described above. This type of optical drive control circuit is well known in the art and can suffer from slow response and long stabilization time.
Therefore, prior art optical disk drives, such as CD and DVD drives, have phase locked-loop control circuits and control methods that do not provide adequate seek times. Furthermore, the stabilization time of the prior art control circuit is too long during the seek mode or during a time when a spindle rotation speed of the optical disk drive changes.